A New Insight on the Indo-Atlantic Exchange Achieved by Indian Ocean Eddies Assessed by Satellite Altimetry and Argo Profiling Float Data.
Abstract:
A recently developed eddy identification and tracking algorithm is applied to daily maps of Absolute Dynamical Topography (ADT) to study the mesoscale activity from the Indian to the Atlantic oceans. The eddy-tracking algorithm has been further improved to account for merging and splitting events. These last two parameters are important because the study region is characterized by a complex eddy dynamics where eddy formation, strong eddy interactions and influence of bottom topography are commonly observed.
Our results suggest that the origin and pathways of Agulhas Rings differ from previous analyses. The earliest positions of the eddies that achieve the Indo-Atlantic exchange are detected as far east as in the Mozambique Channel or southeast of Madagascar while the latest detection can occur in the South-West Atlantic, within the Brazilian Current or even the Zapiola Gyre.
The complex path associated with these eddies is also highlighted: every tracked eddy is shown to interact with other eddies and numerous merging and splitting events occur, especially in the Cape Basin. This affects the eddy trajectories across the Cape Basin: they are not straight and are characterized by a typical residence time between 1 and 2 years, with an actual covered distance 1.5 to 3 times larger than the beeline distance across this region.
Whereas the eddy detection from ADT allows the study of their surface properties along their trajectories, their collocation with Argo profiling floats gives a specific record of their internal structure over the water column. The evolution of the water masses trapped by eddies along their path from the Indian Ocean to Atlantic Ocean is consequently assessed.